Patients who are hypersensitive to derivatives of arsphenamine are usually able to tolerate all pentavalent as well as trivalent arsenicals which do not contain an arsphenamine radical. Both Moore1 and Stokes2 pointed out that tryparsamide seldom leads to a recurrence of a dermatitis originally caused by a trivalent arsenical. The possibility that carbarsone, devegan or other arsenical preparations which are administered orally, rectally or vaginally may cause a recurrence of an arsphenamine dermatitis was not noted in reviewing the literature.
The following cases are reported to illustrate the hazards of prescribing any arsenical preparation for a patient who once had a dermatitis exfoliativa due to arsphenamine without investigating his sensitivity. The existence of hypersensitivity to pentavalent and trivalent arsenicals in the same patient was proved both clinically and by cutaneous tests in the first 2 cases, and the opportunity of observing these 2 cases led to the making